1. Field of the Invention
The present invention relates to an optical inspection station that can inspect the surface of a substrate, such as the glass substrate of a magnetic hard disk.
2. Background Information
Hard disk drives contain a number of magnetic transducers that are coupled to the surfaces of rotating magnetic disks. The transducers can magnetize and sense the magnetic fields of the disks to write and read data as is known in the art. The data is typically stored within concentric annular tracks on the disks.
The transducers are typically integrated into a head that is gimbal mounted to an actuator arm. The actuator arm may include a voice coil motor that can move the heads to the various tracks of the disks.
Each head has an air bearing surface that cooperates with the air flow generated by the rotating disks to create an air bearing between the transducers and the disk surface. The air bearing prevents mechanical wear between the head and the disk surface. It is desirable to optimize the height of each air bearing to maximize the magnetic coupling between the disk surface and the transducers, while preventing mechanical wear between the components.
It is desirable to inspect the disk to insure that there are no defects in the disk surfaces. Defects such as bumps may cause undesirable contact with the heads. There have been developed a number of different inspection systems that can inspect the disk surfaces. For example, U.S. Pat. No. 5,875,029 issued to Jann et al. discloses an optical inspection station that reflects light from a disk surface. The Jann system contains light detectors that can detect the reflected light. The detectors provide input to a computer that can determine the surface characteristics of the light from the detected light.
A magnetic disk typically contains an aluminum substrate that is coated with different layers of magnetic material. There have also been developed magnetic disks that contain a glass substrate. It is desirable to inspect the glass substrate before applying the layers of magnetic material to increase the yield and reduce the cost of producing the disks. It has been found that reflecting light from a glass substrate will produce two images, an image of the top surface and an image of the bottom surface. The image from the bottom surface creates optical noise that distorts the top surface image and degrades the accuracy of the inspection system. It would be desirable to provide an optical inspection system that can more effectively inspect glass substrates than systems of the prior art.